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diff --git a/doc/build-osx.md b/doc/build-osx.md index c9a59bab83..119896dc67 100644 --- a/doc/build-osx.md +++ b/doc/build-osx.md @@ -105,3 +105,103 @@ Notes * Tested on OS X 10.10 Yosemite through macOS 10.13 High Sierra on 64-bit Intel processors only. * Building with downloaded Qt binaries is not officially supported. See the notes in [#7714](https://github.com/bitcoin/bitcoin/issues/7714) + +Deterministic macOS DMG Notes +----------------------------- + +Working macOS DMGs are created in Linux by combining a recent clang, +the Apple binutils (ld, ar, etc) and DMG authoring tools. + +Apple uses clang extensively for development and has upstreamed the necessary +functionality so that a vanilla clang can take advantage. It supports the use +of -F, -target, -mmacosx-version-min, and --sysroot, which are all necessary +when building for macOS. + +Apple's version of binutils (called cctools) contains lots of functionality +missing in the FSF's binutils. In addition to extra linker options for +frameworks and sysroots, several other tools are needed as well such as +install_name_tool, lipo, and nmedit. These do not build under linux, so they +have been patched to do so. The work here was used as a starting point: +[mingwandroid/toolchain4](https://github.com/mingwandroid/toolchain4). + +In order to build a working toolchain, the following source packages are needed +from Apple: cctools, dyld, and ld64. + +These tools inject timestamps by default, which produce non-deterministic +binaries. The ZERO_AR_DATE environment variable is used to disable that. + +This version of cctools has been patched to use the current version of clang's +headers and its libLTO.so rather than those from llvmgcc, as it was +originally done in toolchain4. + +To complicate things further, all builds must target an Apple SDK. These SDKs +are free to download, but not redistributable. +To obtain it, register for a developer account, then download the [Xcode 7.3.1 dmg](https://developer.apple.com/devcenter/download.action?path=/Developer_Tools/Xcode_7.3.1/Xcode_7.3.1.dmg). + +This file is several gigabytes in size, but only a single directory inside is +needed: +``` +Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk +``` + +Unfortunately, the usual linux tools (7zip, hpmount, loopback mount) are incapable of opening this file. +To create a tarball suitable for Gitian input, there are two options: + +Using macOS, you can mount the dmg, and then create it with: +``` + $ hdiutil attach Xcode_7.3.1.dmg + $ tar -C /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/ -czf MacOSX10.11.sdk.tar.gz MacOSX10.11.sdk +``` + +Alternatively, you can use 7zip and SleuthKit to extract the files one by one. +The script contrib/macdeploy/extract-osx-sdk.sh automates this. First ensure +the dmg file is in the current directory, and then run the script. You may wish +to delete the intermediate 5.hfs file and MacOSX10.11.sdk (the directory) when +you've confirmed the extraction succeeded. + +```bash +apt-get install p7zip-full sleuthkit +contrib/macdeploy/extract-osx-sdk.sh +rm -rf 5.hfs MacOSX10.11.sdk +``` + +The Gitian descriptors build 2 sets of files: Linux tools, then Apple binaries +which are created using these tools. The build process has been designed to +avoid including the SDK's files in Gitian's outputs. All interim tarballs are +fully deterministic and may be freely redistributed. + +genisoimage is used to create the initial DMG. It is not deterministic as-is, +so it has been patched. A system genisoimage will work fine, but it will not +be deterministic because the file-order will change between invocations. +The patch can be seen here: [theuni/osx-cross-depends](https://raw.githubusercontent.com/theuni/osx-cross-depends/master/patches/cdrtools/genisoimage.diff). +No effort was made to fix this cleanly, so it likely leaks memory badly. But +it's only used for a single invocation, so that's no real concern. + +genisoimage cannot compress DMGs, so afterwards, the 'dmg' tool from the +libdmg-hfsplus project is used to compress it. There are several bugs in this +tool and its maintainer has seemingly abandoned the project. It has been forked +and is available (with fixes) here: [theuni/libdmg-hfsplus](https://github.com/theuni/libdmg-hfsplus). + +The 'dmg' tool has the ability to create DMGs from scratch as well, but this +functionality is broken. Only the compression feature is currently used. +Ideally, the creation could be fixed and genisoimage would no longer be necessary. + +Background images and other features can be added to DMG files by inserting a +.DS_Store before creation. This is generated by the script +contrib/macdeploy/custom_dsstore.py. + +As of OS X 10.9 Mavericks, using an Apple-blessed key to sign binaries is a +requirement in order to satisfy the new Gatekeeper requirements. Because this +private key cannot be shared, we'll have to be a bit creative in order for the +build process to remain somewhat deterministic. Here's how it works: + +- Builders use Gitian to create an unsigned release. This outputs an unsigned + dmg which users may choose to bless and run. It also outputs an unsigned app + structure in the form of a tarball, which also contains all of the tools + that have been previously (deterministically) built in order to create a + final dmg. +- The Apple keyholder uses this unsigned app to create a detached signature, + using the script that is also included there. Detached signatures are available from this [repository](https://github.com/bitcoin-core/bitcoin-detached-sigs). +- Builders feed the unsigned app + detached signature back into Gitian. It + uses the pre-built tools to recombine the pieces into a deterministic dmg. + |